The present invention relates to liquid crystal displaying apparatus and method of manufacturing a TFT array panel to be used for the same.
Recently the TFT type liquid crystal displaying apparatus with thin film transistor (hereinafter referred to as TFT) mounted on it requires improvements of aperture ratio as well as higher definition and larger image plane.
FIG. 6 is a sectional view showing TFT array substrate of the conventional, general TFT type liquid crystal displaying apparatus. The TFT array substrate is composed of a gate electrode 2, a gate insulating film 3, a semiconductor layer 4 made of amorphous silicon film, an ohmic contact layer 5 made of n+ type amorphous silicon film, a picture element electrode 9 composed of transparent conductive film, a source electrode 10, a drain electrode 11, and a passivation film 14 are formed sequentially on a transparent insulating substrate 1 such as glass substrate or the like. Gate line (not shown) for applying voltage on the gate electrode 2 and a gate electrode 2 to be formed simultaneously with it, or source line (not shown) for applying voltage on the source electrode 10, a drain electrode 11 and a source electrode 10 to be formed simultaneously with them are formed with the use of metal such as Cr, Ti, Ta or the like, which has high resistivity of 20 .OMEGA.Q.cm through 200 .mu..OMEGA..cm.
It is required to form the gate line and gate electrode 2, and source line, source electrode 10 and drain electrode 11 of material with lower resistivity so as to make the pattern finer because of higher resolution and higher aperture ratio of the liquid crystal displaying apparatus, although the gate line and the gate electrode 2, and the source line, the source electrode 10 and the drain electrode 11 are composed of the use of metal with high resistivity in the conventional TFT type liquid crystal displaying apparatus as described above.
For such a reason, Al or alloy with Al as chief component, which is lower in resistivity, lower in cost and easier to make films and to do finer patterning processes is used as material composed of the gate line and the gate electrode 2, and the source line, the source electrode 10 and the drain electrode 11.
But when the Al or the alloy chiefly made of Al is used as the material of the gate line and the gate electrode 2, there is a problem in that etchant including either of hydrochloric acid and ferric chloride, hydrochloric acid and nitric acid, hydriodic acid to be used for patterning of ITO (Indium Tin Oxide) film which is a transparent conductive film for defining a pixel electrode 9 is penetrated through the defective portion of the gate insulating film 3, dust taken into the gate insulating film 3, or the like to corrode the Al for disconnecting the gate line.
For example, as a conventionally proposed method of preventing the corrosion of Al comprising the gate electrode and the gate line by etchant with respect to ITO film, Japanese Unexamined Patent Publication No. 113726/1995 proposes a method of forming the two-layered film structure of Cr/Al having Cr film, protective film, formed on Al film, and Japanese Unexamined Patent Publication No. 268218/1994 proposes a method of forming the gate line and the gate electrode with the use of the two-layered film structure of Al.sub.2 O.sub.3 /Al having alumina on the surface with Al film being anodic oxidized.
Also, Japanese Unexamined Patent Publication No. 129781/1985 proposes a method of preventing the corrosion of Al using solutions of hydrochloric acid or ferric chloride as etchant to be used for patterning of ITO film.
On the other hand, in TFT array composed of a picture element electrode as an uppermost layer, it is required to form protective film such as Cr film or the like on the Al film or the Al alloy film, because a problem is caused in that the etchant to be used in the patterning of ITO film comprising the picture element electrode as in the gate line and the gate electrode described above, is penetrated through interlayer insulator formed between the source line, the source electrode and the drain electrode and ITO film to corrode Al comprising the source line, the source electrode and the drain electrode, when Al film or Al alloy film is used on the surface layer of the source line, the source electrode and the drain electrode which become the lower layer of the picture element electrode through the interlayer insulator.
As described above, though conventionally proposed methods are effective as a method of forming the gate line and the gate electrode using the material with low resistivity without corrosion by etchant to be used in the patterning of ITO film comprising the picture element electrode in TFT array, for example, methods of forming protective films such as Cr film, alumina film anodic oxidized or the like on Al film with the use of Al film as the gate line and the gate electrode had problems in that the forming step of Cr film, the anodic oxidizing step of the Al were required to increase the number of manufacturing steps, further causing an inferior pattern because of sticking of dusts during the halfway step operation so as to reduce the productivity and the yield.
Also, a method of using sulfuric acid solution as etchant for effecting the patterning of ITO film had problems in that the productivity was lower because of lower etching rate of ITO with sulfuric acid solution.
Also, the same problems were caused when the material with low resistivity was used as main components without corrosion by etchant to be used for patterning of the ITO film even in the source line, the source electrode and the drain electrode in TFT array in the construction where the picture element electrode was the uppermost layer.
Accordingly, an object of the invention is to provide a method of manufacturing TFT array which can prevent the corrosion of the material with low resistivity used on the surface layer with the etchant of the ITO film comprising the picture element electrode without reduction in the formation of protective film or in productivity with use of etchant for ITO film low in etching rate even with the use of material with low resistivity in the top layer of the gate line and the gate electrode or the source line, the source electrode and the drain electrode.
Also, another object of the invention is to provide a liquid crystal displaying apparatus, where the pattern is made narrower and the aperture ratio is made higher by using the material with low resistivity as main components the gate line and the gate electrode or the source line, the source electrode and the drain electrode.